Chronic pain, a disease process that is so complex that we are only just beginning to understand its triggers, has recently been gaining recognition as a medical condition on its own. But how does living with chronic pain feel? And how do the body and brain deal with it?
Aching, dull, gnawing, burning, sharp, shooting, piercing…
These are just some of the words people tend to use to describe their pain.
Now imagine you had to endure a bit of this every waking day until you don’t know what it’s like to go about your day without this baseline of pain slowly depleting your mental and physical energy in the background.
That is the reality for many people who deal with chronic pain.
Some days may be great, some days bad; the signs may not always be visible and it may be an inward battle hidden behind gritted teeth and forced smiles.
But how does chronic pain become, well, chronic?
In the latest installment of our In Conversation podcast dedicated to Pain Awareness Month, Medical News Today dives into the science behind chronic pain with Dr. Hilary Guite and Dr. Tony L. Yaksh, professor of anesthesiology and pharmacology at the University of California, San Diego, as Joel Nelson, longtime psoriatic disease and arthritis patient and advocate, shares his personal journey with pain.
Primary and secondary chronic pain
Chronic pain may often be dismissed as purely a symptom of a larger problem or not taken as seriously because it is not life threatening. However, the burden of chronic pain is not only personal but also societal.
StudiesTrusted Source show that people with chronic pain may have difficulty in going about their daily lives and doing activities, as well as have poorer overall health. People with chronic pain may also have to deal with job insecurity or unemployment.
It wasn’t until 2018 that the International Classification of Diseases (ICD) gave chronic pain its own code, in the preliminary version of the new ICD-11 coding systemTrusted Source, paving way for its recognition and diagnosis.
According to the World Health Organization (WHO), chronic pain is now classified into two categories: chronic primary pain and chronic secondary pain.
Primary pain, according to this classification, refers to pain that is not caused by or cannot be explained by another medical condition. Some examples may be fibromyalgia or chronic primary low back pain.
“Fibromyalgia [is] a condition that varies from person to person, but is a widespread pain condition affecting at least 4 to 5 regions of the body and lasts at least 3 months but usually longer. No other cause is found for the pain and it is, therefore, a type of primary chronic pain,” Dr. Guite explained.
Secondary pain, on the other hand, is secondary to or caused by an underlying medical condition. Arthritis, cancer, or ulcerative colitis-related pain would fall within this umbrella.
The very personal experience of chronic pain
“[M]y chronic pain started around 10 years old. And [since] then, chronic pain has kind of been an intermittent part of my life right through to the present day,” Joel Nelson told MNT‘s In Conversation.
Joel is now 38 years old, which means he’s been living with chronic pain for a good few decades.
“[M]y first experience with pain was [when] I got a pain in my hip; it was like a gravelly sort of burning feeling. And it just progressed; the more I used the joint, the [more it got] worse, it got to the point where I [was] sort of losing mobility,” he said.
That was the point he decided to reach out for help—as most people do.
Joel said one word to describe his chronic pain is “noise.”
“I always have described it as noise because on the days when that pain is intense, my ability to absorb other information, deal with multiple things at a time, it’s just gone,” he said.
“Living with my condition today, I think the most important takeaway about the experience is the fluidity of it. [U]ltimately, [my limits and mobility] can range from anything to where I can do more than walking, and I might be able to do a bit of running and cycling like I am currently, to next week I might be back on crutches. [A] lot of that is dictated by pain. So with arthritis, I get a lot of morning stiffness, but it’s the pain that limits my ability to do things.”
— Joel Nelson
Likening it to “a series of chapters,” Joel said it’s not easy to anticipate what will happen next with his chronic pain.
Transitioning from acute to chronic pain
Behind acute pain becoming chronic, scientists have found that a gateway receptor called Toll-like receptor 4Trusted Source (TLR4) may be a controlling factor.
“We know that under a tissue [or nerve] injury of various sorts that we can activate signaling that normally is associated with what we call innate immunity. And one of the mediators of that is something called the toll-like receptor and it turns out that while those are normally there to recognize the presence of foreign bugs, for example, E. coli, those bugs have in their cell membrane, something called lipopolysaccharide, or LPS. We don’t have that normally in our system, but it comes from bacteria,” said Dr. Yaksh.
“You’re born with it, you don’t have to develop it. It’s there all the time. What we’ve come to find out over the last years [t]hat there are many products that your body releases that will [a]ctivate those very same toll-like receptors,” he added.
Toll-like receptors may prime the central immune system for heightened states of pain. In response to harmful stimuli, stressors, or tissue injury, especially in the microbiome or the gastrointestinal tract, the body starts to release products from inflammatory cells.
“When this happens, these products that are released from our own body can [a]ctivate these toll-like receptors, and there’s [one] we call TLR4 [which] is present on inflammatory cells, and it’s also present on sensory neurons,” he explained.
Dr. Yaksh said that activating TLR4 itself doesn’t cause as much pain, but that it sets the nervous system up to become more reactive.
Coupled with this priming, if there are other stressors present at the time—such as a bad diet or psychological distress, pointed out Dr. Guite— this can set off a whole cascade that can fuel this transition to chronic pain.
Is it all in the brain?
Theories so far suggest pain happens at the intersection of where the body meets the brain.
“[Y]our comment about pain [being] in the brain is absolutely the correct way to think about it; the output function of anything comes from the higher centers,” said Dr. Yaksh.
It all boils down to how the brain registers pain when there is tissue damage.
Pain is a crucial function for our survival; it is essentially a warning system that alerts our bodies that there is damage or illness to deal with. After an illness or injury, the nerves surrounding the area start sending signals up to the brain through the spinal cord, which encourages us to get help and stop further damage.
After the body sustains an injury, the damage to the body’s organs and tissues triggers an acute inflammatory response that involves immune cells, blood vessels, and other mediators. However, sometimes, even after this initial injury phase passes and the body heals, the nervous system may stay in this state of distress or reactivity.
When this happens, the body may become hypersensitive to pain. If this increased sensitivity is to heat or touch around the injured area, this is called “peripheral sensitizationTrusted Source.”
“[I]f I were to jam my finger, or if I were to develop, in Joel’s case, an event that leads to a local autoinflammation of the joint, then, in fact, that inflammation leads to the release of factors, which now sensitize the innervation of that joint,” Dr. Yaksh elaborated.
Dr. Yaksh said this is something all people experience, regardless of whether it is chronic pain. He explained that after an injury, however, an innocuous activity such as wiggling one’s finger can “[become] extraordinarily noxious.”
He described this as a sensitization generated by peripheral injury and inflammation, where this information is then relayed to the brain through the spinal cord.